Chemical Capture of Phosphine by a Sol-Gel-Derived Cu/TiO2 Adsorbent - Interaction Mechanisms

In this study, a novel sol gel-derived Cu/TiO2 adsorbent has been demonstrated to exhibit exceptional capacities of 40,62, 49.52, and 108.48 mg PH3/g Cu/TiO2 for the oxidative capture of phosphine (PH3) in N-2, air, and humidified air, respectively. We have proposed the oxidative mechanisms for PH3 on the Cu/TiO2 sample on the basis of elemental, chemical state, functional group, and microstructural analysis. Moreover, the influence of O-2 and water vapor on the capture capacity is discussed. The transformation of PH3 followed the sequence of PH2 -> H2P-OH -> HP(OH)(2) -> P(OH)(3) -> HO-P=O -> H3PO4. At the same time, the CuO/Cu(OH)(2) moieties in the TiO2 lattice were reduced to Cu-0. The H2P-OH and HO-P=O are the two stable intermediates, and they occupied the active species to inhibit further chemisorption. Direct oxidation of PH3 or the intermediates with adsorbed O-2 was not efficient. However, the Cu/TiO2 sample catalyzed their interactions via reduction and then oxidation of the Cu-2+ ions. Water vapor acts as a cocatalyst to facilitate the oxidation of the intermediates. The end product, H3PO4, migrated to bound the TiO2 support and free the CuO/Cu(OH)(2) for the following catalytic processes. Although competitive adsorption of water molecules initially retarded the adsorption rate, the high extent of oxidation greatly promoted the capture capacity of the Cu/TiO2 in humidified air.